Effects of ethanol on fruit selection by frugivorous birds

Abstract

Ethanol is a natural by-product of the fermentation process of fruit sugars. Its production started with the advent of fleshy fruits, which suggests a long-term association between ethanol and frugivores. Consequently, one suggestion is that because frugivores could use its odour to locate fruiting plants, they should show a preference for fruit with high ethanol concentrations. The aim of this study was to test this hypothesis by determining whether frugivorous birds show a preference for fruit laden with alcohol at levels equivalent to those of overripe fruits. Three species of frugivorous bird species were used for this study: the Cape White-eye (Zosterops virens), Speckled Mousebird (Colius striatus) and Red-winged Starling (Onychognathus morio). Birds were provided with two artificial fruit diets in pairwise choice tests: an experimental diet containing 1% ethanol and a control diet with no ethanol. For all species, no significant differences were observed in the amount of artificial fruit consumed between the food types. Given that the concentration of ethanol used in the study is assumed to represent that of overripe fruit, these results, in conjunction with previous studies, suggest that birds do not show a preference for fruits with high ethanol concentrations.